Oxidation inhibitors for lubricant oils



United States Patent This invention relates to novel oxidationinhibitors for hydrocarbon lubricant oils. More particularly, itprovides a unique organosilicon compound having a remarkableeffectiveness for inhibiting such oxidation.

It has now been discovered, pursuant to the invention,

that an outstanding oxidation inhibitor for hydrocarbon lubricant oilscomprises the reaction product of an aldehyde having up to about 20carbon atoms per molecule with silicon disulfide. The reaction product,in addition to its eflicacy for the foregoing purpose, is relativelystable, oil soluble, and producible from low-cost reactants and withminimum difi'iculty.

The starting aldehyde may be any of the relatively low molecular weightaldehydes, that is, having up to about 20 carbon atoms per molecule andhaving the formula RCHO, With the group R which is attached to thecarbonyl group being preferably alkyl, but also alkenyl, substitutedalkyl, aryl, aralkyl, or alkaryl. As illustrative non-limiting examplesof suitable aldehydes there may be mentioned: formaldehyde (which isnot, however, reactable in certain polymeric forms such asparaformaldehyde), acetaldehyde, propionaldehyde, n-butyraldehyde,isobutyraldehyde, n-valeraldehyde, n-caproaldehyde, nheptaldehyde,acrolein, crotonaldehyde, chloral, chloral hydrate, benzaldehyde,tolualdehyde, etc, The aldehyde reactant is advantageously employed inlarge excess over the silicon disulfide.

Anhydrous conditions are apparently preferred during the reaction. Waterevidently decomposes silicon disulfide to a silicon oxide or hydroxideand hydrogen sulfide, thus making it unavailable for the reaction. Atemperature within the range of about 50 to about 150 C., optimallyaround 100-l30 C., is desirably employed, and is maintained for asufficient time to permit substantial cessation of hydrogen sulfideevolution. Temperatures higher or lower than those cited previously maybe employed, although it appears that lower temperatures unduly tend toincrease reaction time while there is no particular advantage inoperating at higher temperatures.

The inventive oxidation inhibitor may be employed in hydrocarbonlubricant oils in concentrations ranging from as low as 0.05 weightpercent to about 3 percent or even higher. The precise concentrationdepends upon the illtrinsic corrosivity of the lubricant oil togetherwith the extent of inhibition desired, and may be determined from sampletests.

Hydrocarbon lubricant oils are generally those naturally orsynthetically derived (e.g., propylene polymer or isobutylene polymeroils) having viscosity ranging from about 20 S.S.U. at 100 F. to about3,000 S.S.U at 210 F. Such oils may contain various other additives suchas detergents, viscosity index improvers, pour points, depressants,extreme pressure additives, foam inhibitors, dyes, etc.

The inventive inhibitors may be evaluated quantitatively by means of theStirring Sand Corrosion Test (S.S.C.T.).

For the S.S.C.T., a copper-lead test specimen is lightly abraded withsteel wool, washed with naphtha, dried and weighed to the nearestmilligram. The cleaned copperlead test specimen is suspended in a steelbeaker, cleaned with a hot tri-sodium phosphate solution, rinsed withwater, acetone and dried, and 250 grams of the oil to be tested,together with 0.625 gram lead oxide and 50 grams 3,222,281 Patented Dec.7, 1965 "Ice of a 30-35 mesh sand charged to the beaker. The beaker isthen placed in a bath or heating block and heated to a temperature of300 F. (plus or minus 2 F.) while the contents are stirred by means of astirrer rotating at 750 rpm. The contents of the beaker are maintainedat this temperature for 24 hours, after which the copper-lead testspeciment is removed, rinsed with naphtha, dried and weighed. The testspecimen is then replaced in the beaker and an additional 0.375 gram oflead oxide added to the test oil. At the end of an additional 24 hoursof test operation the test specimen is again removed, rinsed and driedas before, and weighed. The test specimen is again placed in the beakertogether with an additional 0.250 gram of lead oxide and the testcontinued for another 24 hours (72 hours total). At the conclusion ofthis time, the test specimen is removed from the beaker, rinsed innaphtha, dried and weighed. The loss in weight of the test specimen isrecorded after each weighing. A weight loss of 200 milligrams or less in48 hours and 500 milligrams or less in 72 hours is allowable.

The invention may be illustrated with reference to the followingembodiments, which are intended to illustrate the principles of theinvention but not to be wholly exclusive or definitive with respect toscope or conditions.

Example 1 This example illustrates the preparation of the reactionproduct of silicon disulfide and n-heptaldehyde.

To a flask containing 22.8 grams (0.2 mol) of technical n-heptaldehydeis added 9.2 grams (0.1 mol) of finely powdered silicon disulfide. Themixture is stirred at 110 C. for 5 hours until hydrogen sulfide is nolonger evolved. The hot mixture is filtered and the filtrate evaporatedunder vacuum to remove unreacted nheptaldehyde. The product is agelatinous solid containing 5.0 weight percent silicon.

When added to a heavy-duty SAE, 30 base oil at a concentration of only0.5 weight percent, the additive produced above exhibits a weight lossof only 90.3 milligrams at 48 hours and 88.4 milligrams at 72 hours.

The additive prepared in this example, when contrasted with a somewhatsimilar additive prepared by reacting silicon sulfide withmethyl-n-heptyl ketone is demonstrated by comparing the two productswith respect to their performance under the S.S.C.T. and under thesilver ball Fales test (Journ. Inst. Pet, 32, April 1946); the presentadditive is almost three times as eitective as the ketonepreparedadditive under the conditions of the S.S.C.T., while it is only about afifth as effective in reducing silver wear in the silver Falex test.

Example 2 Example 1 is repeated with acetaldehyde, in an equal molarquantity, substituting for the n-heptaldehyde. The reaction is conductedunder pressure to maintain a liquid phase. Excellent results areobtained under the S.S.C.T.

Example 3 Example 1 is repeated with isobutyraldehyde, a mixture ofn-heptaldehyde with formaldehyde, acrolein, chloral, benzaldehyde, andp-chloro-benzaldehyde. The resultant products are all efiectiveoxidation inhibitors under the conditions of the S.S.C.T.

Thus it is apparent from the foregoing description that there has beenprovided an outstanding oxidation inhibitor for hydrocarbon lubricantoils. While the invention has been described in conjunction with certainembodiments thereof, it is manifest that these are by way ofillustration only, and that various alternatives, modifications, andvariations will become apparent to those skilled in the art in light ofthe foregoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations as fall within thespirit and broad scope of the appended claims.

We claim:

1. A hydrocarbon lubricating oil normally susceptible to oxidationcontaining, in a minor amount suificient to inhibit said oxidation, thereaction product obtained by reacting a C aldehyde and silicon disulfidein a molar ratio of from about 12 moles of said aldehyde per mole ofsaid disulfide under anhydrous conditions at a tempera ture of fromabout 50 to about 150 C. until hydrogen sulfide is no longer evolved,said aldehyde having the formula RCI-IO wherein R is a member of thegroup consisting of alkyl, chloro-substituted alkyl, alkenyl, phenyl,chlorophenyl and tolyl.

2. The lubricant of claim 1 wherein the amount of said reaction productis from about 0.05 to about 3 weight percent.

3. The lubricant of claim 2 wherein R is C alkyl.

4. The lubricant of claim 2 wherein said aldehyde is n-heptaldehyde.

5. The reaction product obtained by reacting a C aldehyde and silicondisulfide in a molar ratio of from about 1-2 moles of said aldehyde permole of said disulfide under anhydrous conditions at a temperature offrom about 50 to about 150 C. until hydrogen sulfide is no longerevolved, said aldehyde having the formula RCHO wherein R is a member ofthe group consisting of alkyl, chloro-substituted alkyl, alkenyl,phenyl, chlorophenyl and tolyl.

6. The composition of claim 5 wherein R is C alkyl.

7. The composition of claim 5 wherein said aldehyde is n-heptaldehyde.

8. The method of preparing a composition suitable for use as anoxidation inhibitor for hydrocarbon lubricating oils which comprisesreacting C aldehyde and silicon disulfide in a molar ratio of from about1-2 moles of said aldehyde per mole of said disulfide under anhydrousconditions at a temperature of from about 50 to about 150 C. untilhydrogen sulfide is no longer evolved, said aldehyde having the formulaRCHO wherein R is a member of the group consisting of alkyl,chlorosubstituted alkyl, alkenyl, phenyl, chloro-phenyl and tolyl; andrecovering the resultant composition.

References Cited by the Examiner UNITED STATES PATENTS 2,588,083 3/1952Burkhard et al. 260448.2

DANIEL E. WYMAN, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

1. A HYDROCARBON LUBRICATING OIL NORMALLY SUSCEPTIBLE TO OXIDATIONCONTAINING, IN A MINOR AMOUNT SUFFICIENT TO INHIBIT SAID OXIDATION, THEREACTION PRODUCT OBTAINED BY REACTING A C1-20 ALDEHYDE AND SILICONDISULFIDE IN A MOLAR RATIO OF FROM ABOUT 1-2 MOLES OF SAID ALDEHYDE PERMOLE OF SAID DISULFIDE UNDER ANHYROUS CONDITIONS AT A TEMPERATURE OFFROM ABOUT 50 TO ABOUT 150*C. UNTIL HYDROGEN SULFIDE IS NOT LONGEREVOLVED, SAID ALDEHYDE HAVING THE FORMULA RCHO WHEREIN R IS A MEMBER OFTHE GROUP CONSISTING OF ALKYL, CHLORO-SUBSTITUTED ALKYL, ALKENYL,PHENYL, CHLOROPHENYL AND TOLYL.